Hello @lucky alqodar ,
Thank you for your update.
Do you mean right click domain name and select "Find"? If so, here are two forests (a.local and b.local with two child domains) with two-way forest trust. I can see the other forest.
If we can not see the other domain, maybe the trust can not be set up successfully. We can remove the trust and refer to the similar case to set up trust again to see if it helps.
setup of trust relationship between 2 domains
https://social.technet.microsoft.com/Forums/windowsserver/en-US/9e501d72-5457-421a-b81b-3a1f83ac7b0e/setup-of-trust-relationship-between-2-domains?forum=winservergen
Best Regards,
Daisy Zhou